1. Field of the Invention
This invention relates to knobs for use with multi-functional control devices, and, more particularly, to an improved knob for use with control devices having push-pull and rotary selectable functions.
2. Description of the Prior Art
In many environments in which space is at a premium, such as in an aircraft cockpit or the like, often control functions are consolidated to be controllable by a single device having a single control knob. For instance, oftentimes a switch or rheostat which has a rotational function may be combined with a push-pull function as well, which may operate separately or in conjunction with the rotary function.
In a typical aircraft cockpit environment, for example, such multi-functional control device may be mounted behind an instrument or display panel with a control shaft extending through it for operation of the control device. Typical display panels have various indicia formed thereon which indicate various positions of the control device or the functions selectable by the control device. Often, back lighting means are provided, such as by a lighted plexiglass sheet or the like over which is placed an opaque panel having apertures or transparent areas forming the desired indicia, so that light passes through the various indicia forming apertures or portions to indicate the various functions at corresponding rotational positions of the control device.
Ordinarily, control knobs include a skirt to cover the unselected indicia having a windowed portion to enable only a particular selected indicia to be seen. The knobs in use typically are of a unitary structure so that to operate the push-pull function of the control device the entire knob is merely pushed into or pulled from the direction of the display panel. The rotational function is selected merely by rotating the knob.
When such knob is pulled from the panel, however, the skirt is raised a distance above the panel from its usual position. This often undesirably permits light from the unselected indicia to be seen from under the skirt over relatively large angles from the display panel. Additionally, in the pulled position, since the relative positions of the indicia and the window of the skirt are changed, the paralax encountered in identifying the particular selected indicia becomes significant. Both of these problems may be undesirable, especially in an aircraft cockpit environment where at night the amount of stray or annoying light must be minimized, and at all times the positive identification of selected functional indicia must be promoted.